Solution and Process to Treat Surfaces of Copper Alloys in Order to Improve the Adhesion Between the Metal Surface and the Bonded Polymeric Material

ABSTRACT

The invention concerns processes and solutions for the treatment of copper alloy surfaces, which are subsequently to be firmly bonded to polymeric material. The solution is used, in particular for firmly bonding lead frames to encapsulating molding compounds (polymeric material). The solution contains an oxidant, at least one acid, at least one adhesion-enhancing compound characterized in that the solution additionally contains fluoride ions in an amount of at least 100 mg per litre and chloride ions in an amount of 5 to 40 mg per litre. The solution is particularly useful for treatment of copper alloy surfaces, containing alloying elements selected from the group consisting of Si, Ni, Fe, Zr, P, Sn and Zn.

The invention concerns a solution and a process to treat copper alloysurfaces so that a tight bond can be subsequently formed between thetreated copper surfaces and polymeric material. The solution preferablyserves to treat surfaces of lead frames made of copper alloys containingalloying elements selected from the group of Si, Ni, Fe, Zr, P, Sn.

In manufacturing lead frames and printed circuit boards alike, varioussteps are carried out in which copper surfaces must be tightly bonded toan organic substrate. In some cases, the required adhesion of the formedbonds must be ensured over a long period. In other cases, a tight bondonly has to exist for a short period, e.g. when a polymeric materialonly remains on the copper or copper alloy surfaces during manufactureof the workpiece.

The easiest way to increase the adhesion is to etch and hence roughenthe copper surfaces before forming the bond. Microetching solutions havelong been used in the production of printed circuit boards and containfor example sulfuric acid solutions of hydrogen peroxide or sodiumperoxodisulfate.

Another procedure is described in U.S. Pat. No. 3,645,772. A treatmentsolution is used for the copper surfaces that e.g. contains5-aminotetrazole.

Long-term stability is especially necessary when encapsulating moldingcompounds (polymeric material) into lead frames.

Various procedures for pretreating printed circuit boards have beendeveloped. Commonly, before lamination an oxide layer on the coppersurfaces is formed. In this process, known as the brown or black oxideprocess, very aggressive reaction conditions are used to form the oxide.A disadvantage of this procedure is that the oxide layer used forenhancing adhesion to the polymeric material is not very resistant toacid and especially to hydrochloric treatment solutions. They are henceattacked in subsequent processes for plating the through-holes in theboards. The adhesive bond is eliminated, and delamination occurs at theattacked sites (pink ring: An externally-visible attack on the blackoxide layer directly next to a hole in printed circuit boards with thediscoloration of the originally black oxide layer.

The above-cited problem is solved by reducing the oxide layer surfacebefore lamination. The reduced black oxide is more stable than normalblack oxide against chemicals used in plating the through-holes. Theadditional reduction step costs a great deal, however. In addition, thechemicals used for reduction are not very resistant to oxidation fromair, so that the useful life of the baths and storage life of thesupplementary chemicals are limited. An attempt to eliminate thisproblem is made in JP A 08097559. The reduced copper oxide layers areprovided with a protective layer by treating them with an aqueoussolution containing an aminothiazole and/or aminobenzothiazole compound.However, the problems of expensive reduction chemicals, their lowresistance to oxidation and the layer's sensitivity to acid are notcompletely eliminated.

Another option for promoting adhesion is to treat the copper surfaceswith an aqueous or alcoholic solution of an azole compound. Such aprocedure is e.g. presented in WO 96/19097 A1. The copper surfaces aretreated with a solution that contains 0.1-20 weight percent hydrogenperoxide, an inorganic acid (e.g. sulfuric acid), an organic corrosioninhibitor (e.g. benzotrizole), and a wetting agent. The hydrogenperoxide etches the copper surface to produce microrough surfaces.

U.S. Pat. No. 5,869,130 describes a process for treating metal surfaceswith a composition comprising an oxidizer, an acid, a corrosioninhibitor, a source of halide ions and optionally a water solublepolymer in order to increase the adhesion of polymeric materials to themetal surface.

U.S. Pat. No. 6,562,149 B1 discloses processes and solutions for thepreliminary treatment of copper surfaces which are subsequently to befirmly bonded to organic substrates. The solution is used, inparticular, for firmly bonding laminated multilayered printed circuitboards and for firmly bonding resists to, the copper surfaces of printedcircuit boards. The solutions contain (a) hydrogen peroxide; (b) atleast one acid; (c) at least one nitrogen-containing, five-memberedheterocyclic compound which does not contain any sulphur, selenium ortellurium atom in the heterocycle; and (d) at least one adhesivecompound from the group consisting of sulfinic acids, seleninic acids,tellurinic acids, heterocyclic compounds containing at least onesulphur, selenium and/or tellurium atom in the heterocycle, andsulfonium, selenonium and telluronium salts.

However, as compared to the printed circuit board production the commonmetallic substrates used fore lead frames are copper alloys with acertain, relatively low amount of alloying elements, required to achievethe mechanical and electrical properties sought.

Some alloys, however, are only partially attacked or with a reducedreaction rate. This leads to unsatisfactory roughness or insolubleresidues or smut on the alloy surface. The result in both cases in a nonoptimized adhesion improvement achieved by the process.

The present invention is therefore based on the problem of avoiding thedisadvantages of the state of the art and finding a treatment solutionand a process that can create a tight bond between the copper alloysurfaces and polymeric material surfaces and is at the same timesuitable to treat a wide range of different copper alloy compositions.The process should be simple, easy to use, and inexpensive. It is alsoimportant that treatment with the solutions produce a material bond thatis not problematic (no smut formation, decomposition of thepre-treatment solution etc.). The used treatment solutions shouldtherefore be particularly suitable for manufacturing lead frames.

This problem is solved by the solution cited in claim 1 and thetreatment process cited in claim 23.

The solution according to the invention is for treating copper alloysurfaces to allow a tight bond to be formed with plastic materials, andit comprises:

-   -   a) an oxidant    -   b) at least one acid    -   c) at least one adhesion-enhancing compound    -   d) fluoride ions in an amount of more than 100 mg per litre    -   e) chloride ions in an amount of 5 to 40 mg per litre.

Adhesion-enhancing compounds are to be selected that are sufficientlysoluble in the acidic, preferably sulfuric acid solution.

The process according to the invention is carried out by bringing thecopper alloy surfaces into contact with the solution.

The solution is also suitable for treatment of copper alloy surfaces,thereafter depositing a second metal layer on the such treated copperalloy surface and finally bond a polymeric material thereto. The secondmetal layer can for example be a deposit of Ni—Pd—Au or Ag, forming asolderable layer.

By roughening the copper alloy surface with a treatment solutionaccording to claim 1, the adhesion properties of the polymeric materialto the second metal layer are also greatly enhanced, which can be seenfrom the Example 4.

Preferred embodiments of the invention are the subject-matter ofdependent claims 2-22.

For example adhesion-enhancing compounds selected from the groupconsisting of triazoles, benzotriazoles, imidazoles, tetrazoles, purinesand mixtures thereof may be used. These compounds react with the copperalloy surfaces to form a protective complex layer.

Preferred tetrazole compounds are 5-aminotetrazole and5-phenyltetrazole. A preferred imidazole compound may be benzimidazole.5-aminotetrazole, 5-phenyltetrazole, benzotriazole, methylbenzotriazoleand ethylbenzotriazole are preferred compounds given their favorablesolubility in the treatment solution and their availability.

Preferred combinations are benzotriazole, methylbenzotriazole,ethylbenzotriazole, 5-aminotetrazole and 5-phenyltetrazole as thenitrogen-containing, heterocyclic compounds with aminothiophenecarboxylic acids, their esters and amides, aminothiazoles andsubstituted aminothiazoles as the heterocyclic compounds.

In order to improve the long-term stability of the bond between themetal surface and the polymeric material, a mixture of at least onenitrogen-containing, five-membered heterocyclic compound that does notcontain sulfur, selenium or tellurium atoms in the heterocycle and atleast one adhesion-promoting compound selected from the group consistingof sulfinic acids, selenic acids, telluric acids, heterocyclic compoundsthat contain at least one sulfur, selenium and/or tellurium atom in theheterocycle, as well as sulfonium, selenonium and telluronium salts,where the sulfonium, selenonium and telluronium salts are compounds ofgeneral formula A:

where A is S, Se or Te, R₁, R₂ and R₃ is alkyl, substituted alkyl,alkenyl, phenyl, substituted phenyl, benzyl, cycloalkyl and substitutedcycloalkyl, where R₁, R₂ and R₃ can be the same or different, and X⁻ isthe anion of an inorganic or organic acid or hydroxide, with the provisothat the acid according to component b) is not identical to a sulfinic,selenic or telluric acid according to component d), is applied.

Preferred sulfinic acids are compounds of chemical formula B:

wherein R₄, R₅ and R₆ are selected from the group consisting ofhydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl and R₇—(CO)— wherein R₇ is hydrogen, alkyl, substituted alkyl, phenyl orsubstituted phenyl, where R₄, R₅ and R₆ can be the same or different.

It is preferable for the solution to contain formamidine sulfinic acid.Preferable aromatic sulfinic acids are benzene sulfinic acid, toluenesulfinic acids, chlorobenzene sulfinic acids, nitrobenzene sulfinicacids and carboxybenzene sulfinic acids.

Other preferable adhesion-promoting heterocyclic compounds arethiophene, thiazole, isothiazole, thiadiazole and thiatriazole.

Suitable thiophenes are compounds of chemical formula C:

wherein R₈, R₉, R₁₀, R₁₁ are selected from the group consisting ofhydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl, halogen,amino, alkylamino, dialkylamino, hydroxy, alkoxy, carboxy, carboxyalkyl,alkoxycarbonyl, aminocarbonyl and R₁₂ —CONH— wherein R₁₂ is hydrogen,alkyl, substituted alkyl, phenyl or substituted phenyl, where R₈, R₉,R₁₀ and R₁₁ can be the same or different and can be a part of the homo-or heterocyclic ring condensed onto the thiophene ring.

Particularly preferred thiophenes are aminothiophene carboxylic acids,their esters and amides. For example, 3-aminothiophene-2-carboxylic acidmethyl ester can be advantageously used.

Suitable thiazoles are compounds of chemical formula D:

wherein R₁₃, R₁₄, R₁₅ are selected from the group consisting ofhydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl, halogen,amino, alkylamino, dialkylamino, hydroxy, alkoxy, carboxy, carboxyalkyl,alkoxycarbonyl, aminocarbonyl and R₁₆ —CONH— wherein R₁₆ is hydrogen,alkyl, substituted alkyl, phenyl or substituted phenyl, where R₁₃, R₁₄and R₁₅ can be the same or different and can be a part of the homo- orheterocyclic ring condensed onto the thiazole ring.

Particularly suitable thiazoles are aminothiazole and substitutedaminothiazole.

Other preferred thiadiazole adhesion-promoting compounds are from thegroup consisting of aminothiadiazoles and substituted aminothiadiazoles.

In addition, the preferred sulfonium salts are salts oftrimethylsulfonium, triphenylsulfonium, methionine alkylsulfonium andmethionine benzylsulfonium.

The nitrogen-containing, five-member heterocyclic compounds that do notcontain any sulfur, selenium or tellurium atom in the heterocycle can bemonocyclic and polycyclic condensed ring systems. For example, thecompounds can contain an anellated benzene, naphthalene or pyrimidinering provided that they are sufficiently soluble in the acid solution.It is preferable for the solution to contain triazoles, tetrazoles,imidazoles, pyrazoles and purines or their derivatives.

In particular, the solution contains triazoles of chemical formula E1:

wherein R₁₇, R₁₈ are selected from the group consisting of hydrogen,alkyl, substituted alkyl, amino, phenyl, substituted phenyl andcarboxyalkyl, where R₁₇ and R₁₈ can be the same or different and can bea part of the homo- or heterocyclic ring condensed onto the triazolering.

Benzotriazole, methylbenzotriazole, ethylbenzotriazole anddimethylbenzotriazole are particularly preferable.

In addition, the solution can contain tetrazoles of chemical formula E2:

wherein R₁₉ is selected from the group consisting of hydrogen, alkyl,substituted alkyl, halogenalkyl, amino, phenyl, substituted phenyl,benzyl, carboxy, carboxyalkyl, alkoxycarbonyl, aminocarbonyl and R₂₀—CONH wherein R₂₀ is hydrogen, alkyl, substituted alkyl, phenyl orsubstituted phenyl.

Preferred tetrazole compounds are 5-aminotetrazole and5-phenyltetrazole. A preferred imidazole compound may be benzimidazole.5-aminotetrazole, 5-phenyltetrazole, benzotriazole, methylbenzotriazoleand ethylbenzotriazole are preferred compounds given their favorablesolubility in the treatment solution and their availability.

Preferred combinations are benzotriazole, methylbenzotriazole,ethylbenzotriazole, 5-aminotetrazole and 5-phenyltetrazole as thenitrogen-containing, heterocyclic compounds with aminothiophenecarboxylic acids, their esters and amides, aminothiazoles andsubstituted aminothiazoles as the heterocyclic compounds.

The process according to the invention is an extremely easy way to treatcopper alloy surfaces to allow them to tightly bond with polymericmaterials. Basically one step is necessary, i.e., treating the copper orcopper alloy surface with the solution according to the invention toallow them to bond with polymeric materials. The adhesion does notdecrease even after a long time. Particularly preferred solutions arethe subject-matter of claim 7.

The advantageous effect of the solution according to the invention wassurprising since it was found that relatively small amounts of chlorideand bromide of 50 mg/l and above already strongly reduce thefunctionality of the etching solution. Applying such solutions isdisclosed in the prior art (U.S. Pat. No. 5,869,130) for treating coppersurfaces but is not suitable to etch copper alloy surfaces which is thesubject of the present invention.

In contrast, the addition of fluoride improves the complete attack ontothese alloys and leads to the desired roughness properties of the copperalloy surface. Alloys containing Si in particular, are most effectivelytreated, as the Si smut on the surface as well as in the solution isremoved within the etching solution itself. Without the addition offluoride, insoluble residues are formed, which lead to low adhesionvalues and uneven appearance, not acceptable in lead framemanufacturing. Furthermore the alloying elements often result in adecrease of the stability of the treatment solution. Dissolved iron forexample catalyses the decomposition of hydrogen peroxide. Surprisingly,addition of fluoride prevents such decomposition while in contrastchloride and bromide do not reduce the decomposition rate of thetreatment solution.

The properties of lead frame alloy surfaces become more and moreimportant as a result of the lead free soldering applications for theelectronic industry. Lead free soldering generates higher temperaturesto the electronic components. Because of higher soldering temperaturesthe risk of the “popcorn effect” rises. This effect arises, whenhumidity penetrates the device and the water evaporates explosively uponheating during the post-treatment steps and destroys the bond betweenthe polymeric material and the metal surface. This effect destroyselectronic devices. A good adhesion of the polymeric material to themetal substrate minimizes the risk of the “popcorn effect” to occur.

As a result of the good adhesion gained by applying the solutionaccording to the present invention, no air moisture can penetrate intothe interface polymeric material/metal substrate.

The fluoride ion amount additionally affects the etch rate of the metalsurface. In a certain range increase in the fluoride ion concentrationresults in an increased etch rate. Applying the solution according toExample 1 with a sodium fluoride concentration of 2.5 g/l results in anetch rate of 1.0 μm/min. If the solution contains 5.0 g/l sodiumfluoride the etch rate is increased to 1.6 μm/min. Thereafter, furtherincreasing the fluoride ion concentration does not affect the etch ratesignificantly. It has to be pointed out that the optimum amount offluoride ions for a given metal depends on its composition and can bedetermined individually by standard measurement methods.

As mentioned above, the solution according to the present invention alsocomprises chloride ions in an amount of 5 to 40 mg per litre. It wasdiscovered that the chloride ions have a beneficial effect on theroughness of the surface to which the solution according to the presentinvention is applied. Particularly good results are obtained when theconcentration of chloride ions is in the range of 15 to 25 mg per litre.

In the present invention the adhesion between the alloy substrate andthe polymeric material is measured quantitatively in values N/mm².

The peel strength was measured by pushing “Mold tablets” after curingand hardening, with a contact area to the test surface of 10 mm² with aDage 4000 equipment, using a shear speed of 0.2 mm/s. The test wasperformed at 20° C.

In the production of lead frames, an important and widely usedSi-containing alloy is C7025. Besides Cu and Ni it contains up to 1.2%of silicon.

Another alloy which is particularly preferred for use in the presentinvention is C194. It contains 97% of Cu, 2.3% of Fe and 0.1% of Mn.Like the above mentioned C7025 alloy, C194 is used in the production oflead frames.

The copper alloy surfaces should first be cleaned to ensure that thetreatment is effective. Any conventional cleaning solution can be used.Normally, wetting agents and sometimes complexing agents (such astriethanol-amine)-containing aqueous solutions are used.

After the cleaned copper alloy surfaces are rinsed, they can be broughtinto contact with a so-called predipping solution that contains one ofthe five-membered heterocyclic compounds dissolved in water, preferablyat a concentration of 0.1-10 g/l, and especially 0.5-2 g/l. Thistreatment helps the adhesion-promoting layer to be formed in thesubsequent treatment step. In particular, any delays in the formation ofthe layer are avoided. The layer starts forming directly when thesurface contacts the solution of the invention.

The surfaces are then treated with the solution according to theinvention without being rinsed beforehand.

The microetching by the oxidant, preferably hydrogen peroxide inconnection with the acid yields microrough copper alloy surfaces. Sincethis increases the surface area, the subsequent adhesion of the copperalloy surfaces to the polymeric material also increases. The change incolor of the surface during treatment is caused by a thin copper oxidelayer. It is preferable for the acid in the solution according to theinvention to be an inorganic acid, and especially sulfuric acid. Otheracids can of course be used.

The treatment is preferably carried out at 20-60° C. The treatment timeis preferably 10-600 sec. The higher the temperature, the faster-actingthe solution. The treatment times can hence even be much shorter. From apractical standpoint, a preferable average temperature would be 35-45°C. to better control the reaction. Average treatment times are 20-90sec. In addition, a top temperature limit may have to be set due topossible incompatibilities between certain solution components at hightemperatures, e.g., wetting agents that have difficulty dissolving athigh temperatures.

The preferable concentration ranges in the solution are:

Sulfuric acid, conc. 10-250 g/l Hydrogen peroxide, 30 weight percent1-100 g/l Adhesion-enhancing compound: triazoles, benzotriazoles,imidazoles, 0.5-50 g/l tetrazoles and mixtures thereof purines 0.5-50g/l

Further components:

Sulfinic, selenic and/or telluric acid 0.05-10 g/l Adhesion-promotingheterocyclic 0.05-20 g/l compound Sulfonium, selenonium 0.01-10 g/land/or telluronium salts fluoride ions 0.2-25 g/l, more preferred 1-10g/l, most preferred 2-5 g/l Chloride ions 5-40 mg/l, preferably 15-25mg/l

After they are treated with the solution according to the invention, thecopper surfaces are rinsed. Then they are dried, e.g. with hot air.

The workpieces, for example lead frames, with the copper or copper alloysurfaces can be treated in conventional dipping systems.

The following examples serve further to clarify the invention:

EXAMPLE 1

An aqueous solution was created by mixing the following components:

Sulfuric acid, 96 weight percent 50 ml Hydrogen peroxide, 40 ml 30weight percent in water Benzotriazole 10 g Formamidine sulfinic acid 0.5g Sodium fluoride 5.0 g Sodium chloride 33 mg Deionized water added to 1l.

The solution was heated to 40° C., and a copper alloy surface (leadframe C7025) containing Cu, Ni (2.2-4.2%), Si (0.25-1.2%) and smallamounts of Mg and Zn was dipped in the solution for 60 sec. After beingtreated, the alloy was rinsed with deionized water and finally dried.

Thereafter as polymeric material a commercially available mold (KMC-289,Shinetsu) was applied to such treated alloy surface, dried and hardenedat a temperature of 175° C.

The peel strength of the lead frame was measured by a button shear test.An adhesion value of 18.5 N/mm² was found. The measured roughness,expressed in RSAI (Relative Surface Area Increase) was 44%±3%(absolute).

COMPARATIVE EXAMPLE 2

Example 1 was repeated with a solution that did not contain sodiumfluoride.

The lead frame surface shows black smut which can easily be taken awayby finger wiping. On this sample a peel adhesion value of only 9.1 N/mm²was obtained. The measured roughness was 42%±3% (absolute).

COMPARATIVE EXAMPLE 3

Example 1 was repeated with a solution that did not contain sodiumchloride.

The lead frame surface shows not black smut, but the roughness wasreduced to lower than 12% RSAI. The peel adhesion value was always below5 N/mm².

EXAMPLE 4

An aqueous solution was created by mixing the following components:

Sulfuric acid, 96 weight percent 50 ml Hydrogen peroxide, 40 ml 30weight percent in water Benzotriazole 10 g Formamidine sulfinic acid 0.5g Sodium fluoride 5.0 g Sodium chloride 33 mg Deionized water added to 1l.

The solution was heated to 40° C., and a copper alloy surface (leadframe C7025) containing Cu, Ni (2.2-4.2%), Si (0.25-1.2%) and smallamounts of Mg and Zn was dipped in the solution for 60 sec. After beingtreated, the alloy was rinsed with deionized water and finally dried.

Thereafter, a layer of Ni—Pd—Au was deposited on the treated copperalloy surface utilizing a commercially available metallization process(Atotech Deutschland GmbH).

Soak cleaner 50° C.  3 min Rinsing Cath. Degreaser 40° C. 60 sec Rinsing5% H2SO4 Nickel sulphamat HS 60° C. 40 sec (thickness of deposited Ni-Rinsing layer ~0.7 μm) Pallacor PPF 35° C.  2 sec (thickness ofdeposited Pd- Rinsing layer ~0.03 μm) Aurocor PPF 35° C.  1 sec(thickness of deposited Au- Rinsing, drying layer ~0.005 μm)

Finally, as polymeric material a commercially available mold (KMC-289,Shinetsu) was applied to such treated alloy surface, dried and hardenedat a temperature of 150° C.

An adhesion value was achieved which is slightly smaller than thataccording to Example 1.

COMPARATIVE EXAMPLE 5

Example 4 was repeated but with a solution that did not contain sodiumfluoride.

The lead frame surfaces shows smut residues and had therefore to becleaned in an additional post treatment step utilizing 50 ml/l H₂SO₄96%, 20 g/l sodium peroxodisulfate and 4 g/l sodium fluoride instead of5% H₂SO₄ prior to metallization with Ni—Pd—Au. As a result only a poorpeel adhesion value was obtained.

1-25. (canceled)
 26. A solution for treating a surface of copper alloysto improve adhesion of polymeric materials thereto, comprising a) anoxidant b) at least one acid c) at least one adhesion-enhancing compoundselected from the group consisting of triazoles, benzotriazoles,imidazoles, tetrazoles, purines and a compound which is a mixture of atleast one nitrogen-containing, five-membered heterocyclic compound thatdoes not contain sulfur, selenium or tellurium atoms in the heterocycleand at least one compound selected from the group consisting of sulfinicacids, selenic acids, telluric acids, heterocyclic compounds thatcontain at least one sulfur, selenium and/or tellurium atom in theheterocycle, as well as sulfonium, selenonium and telluronium salts,where the sulfonium, selenonium and telluronium salts are compounds ofgeneral formula A:

where A is S, Se or Te, R₁, R₂ and R₃ are selected from the groupconsisting of alkyl, substituted alkyl, alkenyl, phenyl, substitutedphenyl, benzyl, cycloalkyl and substituted cycloalkyl, where R₁, R₂ andR₃ can be the same or different, and X⁻ is the anion of an inorganic ororganic acid or hydroxide, with the proviso that the acid according tocomponent b) is not a sulfinic, selenic or telluric acid according tocomponent c) characterized in that the solution additionally contains:d) fluoride ions in an amount of at least 100 mg per litre, e) chlorideions in an amount of 5 to 40 mg per litre.
 27. The solution according toclaim 26, characterized in that the triazole has the following chemicalformula E1:

wherein R₁₇, R₁₈ are selected from the group consisting of hydrogen,alkyl, substituted alkyl, amino, phenyl, substituted phenyl andcarboxyalkyl, where R₁₇ and R₁₈ can be the same or different and can bea part of the homo- or heterocyclic ring condensed onto the triazolering.
 28. The solution according to claim 26, characterized in that thetriazole is selected from the group consisting of benzotriazole,methylbenzotriazole, ethyl benzotriazole and dimethylbenzotriazole. 29.The solution according to claim 26, characterized in that the tetrazolehas the following chemical formula E2:

wherein R₁₉ is selected from the group consisting of hydrogen, alkyl,substituted alkyl, halogenalkyl, amino, phenyl, substituted phenyl,benzyl, carboxy, carboxyalkyl, alkoxycarbonyl, aminocarbonyl and R₂₀—CONH wherein R₂₀ is hydrogen, alkyl, substituted alkyl, phenyl orsubstituted phenyl.
 30. The solution according to claim 29,characterized in that the tetrazole is selected from the groupconsisting of 5-aminotetrazole and 5-phenyltetrazole.
 31. The solutionaccording to claim 26, characterized in that it contains sulfinic acidsselected from the group consisting of aromatic sulfinic acids andcompounds of chemical formula B:

wherein R₄, R₅ and R₆ are selected from the group consisting ofhydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl and R₇—(CO)— wherein R₇ is hydrogen, alkyl, substituted alkyl, phenyl orsubstituted phenyl, where R₄, R₅ and R₆ can be the same or different.32. The solution according to claim 26, characterized in that itcontains formamidine sulfinic acid.
 33. The solution according to claim26, characterized in that it contains aromatic sulfinic acids selectedfrom the group consisting of benzene sulfinic acid, toluene sulfinicacids, chlorobenzene sulfinic acids, nitrobenzene sulfinic acids andcarboxybenzene sulfinic acids.
 34. The solution according to claim 26,characterized in that it contains at least one heterocyclic compoundselected from the group consisting of thiophenes, thiazoles,isothiazoles, thiadiazoles and thiatriazoles.
 35. The solution accordingto claim 34, characterized in that it contains at least one thiopheneselected from the group consisting of compounds of chemical formula C:

wherein R₈, R₉, R₁₀, R₁₁ are selected from the group consisting ofhydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl, halogen,amino, alkylamino, dialkylamino, hydroxy, alkoxy, carboxy, carboxyalkyl,alkoxycarbonyl, aminocarbonyl and R₁₂ —CONH— wherein R₁₂ is hydrogen,alkyl, substituted alkyl, phenyl or substituted phenyl, where R₈, R₉,R₁₀ and R₁₁ can be the same or different and can be a part of the homo-or heterocyclic ring condensed onto the thiophene ring.
 36. The solutionaccording to claim 34, characterized in that it contains at least onethiophene selected from the group consisting of aminothiophenecarboxylic acids, their esters and amides.
 37. The solution according toclaim 34, characterized in that the thiazole is selected from the groupconsisting of compounds of chemical formula D:

wherein R₁₃, R₁₄, R₁₅ are selected from the group consisting ofhydrogen, alkyl, substituted alkyl, phenyl, substituted phenyl, halogen,amino, alkylamino, dialkylamino, hydroxy, alkoxy, carboxy, carboxyalkyl,alkoxycarbonyl, aminocarbonyl and R₁₆ —CONH— wherein R₁₆ is hydrogen,alkyl, substituted alkyl, phenyl or substituted phenyl, where R₁₃, R₁₄and R₁₅ can be the same or different and can be a part of the homo- orheterocyclic ring condensed onto the thiazole ring.
 38. The solutionaccording to claim 34, characterized in that the thiazole is selectedfrom the group consisting of aminothiazoles and substitutedaminothiazoles.
 39. The solution according to claim 34, characterized inthat the thiadiazole is selected from the group consisting ofaminothiadiazoles and substituted aminothiadiazoles.
 40. The solutionaccording to claim 26, characterized in that the sulfonium salt isselected from the group consisting of trimethylsulfonium salts,triphenylsulfonium salts, methionine alkyl sulfonium salts andmethionine benzyl sulfonium salts.
 41. The solution according to claim26, characterized in that the nitrogen-containing, five-memberedheterocyclic compound is selected from the group consisting oftriazoles, tetrazoles, imidazoles, pyrazoles and purines.
 42. A solutionaccording to claim 26, wherein the amount of fluoride ions is at least0.5 g/l
 43. A solution according to claim 26, wherein the amount offluoride ions is at least 2.0 g/l.
 44. A solution according to claim 26,characterized in that the fluoride ions are from a source selected fromthe group consisting of sodium fluoride, potassium fluoride, ammoniumfluoride and tetrafluoro boric acid.
 45. The solution according to claim26, characterized in that sulfuric acid is selected to be the acid forcomponent b) in the solution.
 46. The solution according to claim 26,characterized in that the amount of chloride ions is 15 to 25 mg perlitre.
 47. A process to pretreat copper alloy surfaces to allow a tightbond to be subsequently formed between the copper alloy surfaces andpolymeric material in which the copper surfaces are brought into contactwith the solution according to claim
 26. 48. A process to pretreatcopper alloy surfaces according to claim 47 characterized in that thecopper alloy contains at least one alloying element selected from thegroup consisting of Si, Ni, Fe, Zr, P, Sn and Zn.
 49. A processaccording to claim 48 wherein the copper alloy surface is on a leadframe and pretreated to create a tight bond between the copper alloylayers and moulding compounds.